Commit 3dfc813d authored Jul 04, 2009 by David Woodhouse

intel-iommu: Don't use identity mapping for PCI devices behind bridges

Our current strategy for pass-through mode is to put all devices into
the 1:1 domain at startup (which is before we know what their dma_mask
will be), and only _later_ take them out of that domain, if it turns out
that they really can't address all of memory.

However, when there are a bunch of PCI devices behind a bridge, they all
end up with the same source-id on their DMA transactions, and hence in
the same IOMMU domain. This means that we _can't_ easily move them from
the 1:1 domain into their own domain at runtime, because there might be DMA
in-flight from their siblings.

So we have to adjust our pass-through strategy: For PCI devices not on
the root bus, and for the bridges which will take responsibility for
their transactions, we have to start up _out_ of the 1:1 domain, just in
case.

This fixes the BUG() we see when we have 32-bit-capable devices behind a
PCI-PCI bridge, and use the software identity mapping.

It does mean that we might end up using 'normal' mapping mode for some
devices which could actually live with the faster 1:1 mapping -- but
this is only for PCI devices behind bridges, which presumably aren't the
devices for which people are most concerned about performance.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

parent 6941af28

drivers/pci/intel-iommu.c

+30 −0

Original line number	Diff line number	Diff line
		@@ -2122,6 +2122,36 @@ static int iommu_should_identity_map(struct pci_dev *pdev, int startup)
		if (iommu_identity_mapping == 2)
		return IS_GFX_DEVICE(pdev);

		/*
		* We want to start off with all devices in the 1:1 domain, and
		* take them out later if we find they can't access all of memory.
		*
		* However, we can't do this for PCI devices behind bridges,
		* because all PCI devices behind the same bridge will end up
		* with the same source-id on their transactions.
		*
		* Practically speaking, we can't change things around for these
		* devices at run-time, because we can't be sure there'll be no
		* DMA transactions in flight for any of their siblings.
		*
		* So PCI devices (unless they're on the root bus) as well as
		* their parent PCI-PCI or PCIe-PCI bridges must be left _out_ of
		* the 1:1 domain, just in _case_ one of their siblings turns out
		* not to be able to map all of memory.
		*/
		if (!pdev->is_pcie) {
		if (!pci_is_root_bus(pdev->bus))
		return 0;
		if (pdev->class >> 8 == PCI_CLASS_BRIDGE_PCI)
		return 0;
		} else if (pdev->pcie_type == PCI_EXP_TYPE_PCI_BRIDGE)
		return 0;

		/*
		* At boot time, we don't yet know if devices will be 64-bit capable.
		* Assume that they will -- if they turn out not to be, then we can
		* take them out of the 1:1 domain later.
		*/
		if (!startup)
		return pdev->dma_mask > DMA_BIT_MASK(32);